1. Field of the Invention
This invention relates generally to magnetic recording systems, like magnetic recording disk drives, and more particularly to an all-optical magnetic recording system that does not require an external magnetic field to switch the magnetization of the data bits.
2. Description of the Related Art
The more recent commercially available magnetic recording hard disk drives use perpendicular recording disks, wherein the magnetized regions are oriented perpendicular to the plane of the recording layer of the disk. The conventional perpendicular magnetic recording disk is a “continuous-media” (CM) disk wherein the recording layer is a continuous layer of magnetic material with perpendicular magnetic anisotropy that becomes formed into concentric data tracks containing the magnetically recorded data bits when the write head writes on the magnetic material. The read/write head is located on an air-bearing slider that is supported above the smooth disk surface on a thin film of air or “air-bearing” as the disk rotates.
Perpendicular magnetic recording disks with “bit-patterned media” (BPM) have been proposed to increase the data density. In BPM disks, the magnetic material on the disk is patterned into small isolated data islands such that there is a single magnetic domain in each island or “bit”. The single magnetic domains can be a single grain or consist of a few strongly coupled grains that switch magnetic states in concert as a single magnetic volume. This is in contrast to conventional CM disks wherein a single “bit” may have multiple magnetic grains separated by segregant material. To produce the required magnetic isolation of the patterned islands, the magnetic moment of the spaces between the islands must be destroyed or substantially reduced so as to render these spaces essentially nonmagnetic. In one type of BPM disk, the data islands are elevated, spaced-apart pillars that are separated by nonmagnetic trenches or recesses.
For both CM and BPM disks, the magnetized regions or the individual data islands have their magnetizations switched by an external magnetic field from the disk drive's write head. Because it is known that the recorded magnetizations can experience thermal instability, magnetic recording material with high magneto-crystalline anisotropy may be required. However, this type of material has a high coercivity which requires a high external write field, typically beyond the field that can be achieved by current disk drive write heads. Since it is known that the coercivity of the magnetic material is temperature dependent, one proposed solution to the thermal stability problem is thermally-assisted recording (TAR), sometimes also called heat-assisted magnetic recording (HAMR), wherein the high magneto-crystalline anisotropy material is heated locally to near or above its Curie temperature to lower the coercivity enough so that the external magnetic field from the write head can switch the magnetization. Several TAR approaches have been proposed, such as incorporating on the slider near the write head either an electrically resistive heater or an optical channel with an aperture that emits laser radiation to heat the magnetic recording material while it is exposed to the write field. However, these TAR systems are complex and require complicated fabrication processes to incorporate all the required elements into the slider.
What is needed is a magnetic recording system that does not require a write head to provide an external magnetic field to switch the magnetization of the recorded bits.